Suction controls are routinely used in hospitals to regulate the level of suction delivered from a central supply system to the patient. Patient safety requires the high vacuum from the central supply be regulated to a lower safe level and adjustable for any number of clinical needs. On its most basic level, suction is used to remove fluids and debris from body cavities and is employed in virtually any location where a patient is present. Modern hospitals employ central suction systems with distributed supply at the patient bed. Mechanical controls reduce the high vacuum levels present in the central suction system to lower levels safe for patients and suitable for the patient collection devices. Collection devices are typically plastic, disposable devices that are used to accumulate fluids and debris. The collection devices are located between the point of collection and the control device and serve to protect the piping system and manual controls from contamination by bodily substances.
The suction control mechanism that interfaces high vacuum in the central suction system with the patient contact collection systems are typically reusable mechanical devices. Though application of suction to patients generally results in dedicated one way flow of material away from the patient, there are clinical applications such as drainage from the stomach that necessitate periodic relief of vacuum pressures while in contact with patient.
Unlike other fluidic systems in the hospital, such as oxygen, nitrogen, or medical air, the inlet to the suction system is proximal to the patient and may not be filtered. Typical hospital suction systems utilize a canister to act as a fluidic trap. This canister is typically located between the patient and the suction control. In addition to providing gravimetric or centrifugal separation of liquids and gases, this canister may contain a mechanical float and/or hydrophobic membrane to handle an overflow condition. The failure to use a canister or the failure of the internal overflow mechanisms of the canister may also cause liquids, solids, and suspensions to enter the suction control and hospital suction system.
In addition to room air, caregivers may introduce foreign material or fluids into the flow path. This foreign material may include, singly or in combination:                Vapors        Aerosols        Caustic and or Acidic fluids        Dust, lint and fine particulate matter        Liquids        Solids        Suspensions containing solids/liquid components        Microorganisms        
Any failure of the hospital collection system, such as an overfilled canister, perforated hydrophobic membrane, or sticking gravity float, will cause foreign material to enter the suction regulator. Incorrect setup of the patient collection circuit or unintentional acts by the caregiver can also bypass these safety measures.
Any foreign material that enters the internal flow path of a suction control can affect the system's ability to properly regulate the high levels of suction delivered from the central suction system to clinically safe levels. Infiltration of foreign matter can also render the system inoperable.
Some overflow systems fail to restrict the entry of aerosols into the suction control. These aerosol mixtures may bypass the safety mechanisms of the canister system and find their way to the operable parts of the suction control where the buildup may lead to degradation in the performance of the suction control.
A typical failure mode of a suction regulator is for a bolus of biological fluid to be aspirated into the regulator by accident, followed by a period where low relative humidity room air is drawn in. The dry air flow causes the fluid to dry out resulting in a sticky coating covered with lint and dust. Over time if not properly serviced, these accumulations progress until, layer by layer, system performance is compromised or the system may be disabled.
Filters are used to effectively control aerosols from entering controls, but filters have the limitation of becoming progressively occluded with particles and liquids and require frequent replacement in order to maintain acceptable flow levels. Filters also do not fail in a safe mode in that when clogged, the regulator may indicate that suction is being applied to the patient when in fact the clogged filter is preventing the application of suction to the patient. The failure to apply suction, especially in an emergency is a risk associated with medical suction controls.
Suction systems in the hospital pose five distinct risks to patient safety                1. Application of excessive levels of suction (>300 mmHg) can rapidly precipitate localized barotraumas where the suction has been applied to the patient.        2. Mildly excessive suction, above normal venous return pressures (150 mmHg-300 mmHg) can limit tissue perfusion causing localized tissue necrosis during prolonged application.        3. The inability to deliver adequate static pressure and flow can limit a caregiver's ability to remove blood and vomitus from a patient's oral pharanx and establish a patent airway during emergency procedures.        4. The failure of an intermitting suction circuit in naso-gastric procedures to cycle on and off can expose the lining of the stomach to continuous suction and localized barotraumas. Over extended periods of time, this continuous suction will erode the protective lining of the stomach resulting in ulcerations in the highly vascularized tissues.        5. The inability of a regulator to maintain a stable regulated vacuum characterized by two conditions: Drift, a tendency for the set-point to change over time; and Spike, the tendency to apply significantly greater levels of suction pressure as flow is restricted due to the contact with tissue in the patient catheter, either of these two conditions will prevent the physician prescribed level of suction from being applied to the patient.        
The most common cause of failure in hospital suction controls is the entrance of foreign material into the regulation mechanism of the circuit. Therefore, in the interests of reliability and performance there is a need to limit or prevent foreign materials from entering the pressure regulation mechanism of a suction control apparatus.